B. M, Brydone — Further Notes on the Trimmingham Chalk. 17 



Should it ever be ascertained that there ^s a point at which the 

 forms above mentiojied all disappear, that point may safely be taken 

 as the upper limit of the B. mucronata zone of Norfolk. [I do not say 

 'Norwich Chalk,' because I have a very strong opinion that that 

 term is wholly unscientific. If it implies, as presumably it does, 

 that all the chalk which has ever been exposed within two or three 

 miles of Norwich is of the same zone, that zone must be the zone of 

 B. mucronata, and the term 'Norwich Chalk' is a mere synonym. 

 It is undoubtedly the fact that the sections now accessible (Trowse, 

 Thorpe, and Whitlingham) are all in chalk which contains B. mucro- 

 nata freely, and cannot on any pretext be assigned to any other zone. 

 But many of the fossils recorded from the ' Norwich Chalk,' e.g. the 

 Cephalopoda, seem decidedly unlikely to occur in such chalk as that 

 now exposed, and probably the chalk in which Baculites was 

 abundant was very different stuff from that now to be seen. In that 

 case the * Norwich Chalk ' is a ' hotchpotch ' of an unknown number 

 of zones which should, with its so-called fauna, be discarded as soon 

 as possible in all attempts at zonal classification. I have really very 

 little doubt as to the danger involved in treating the Norwich Chalk 

 as a zonal unit, and many of the peculiar species would probably 

 find a place as synonyms if Samuel Woodward's types could be 

 found. Some can be so treated from the plates; e.g., Serpula 

 accumulata is almost certainly a synonym of S. vortex, S. pentangulata 

 of S. canteriata, S. carinata of S.fluctuata, S. contracta oi S. gordialis 

 (if Professor Deecke rightly identified the specimens to which he 

 assigned the latter name, which has not been very freely admitted 

 by other collectors), and Flagiostoma granulosum of Lima granulata. 

 At any rate, we are not warranted by any accessible information in 

 taking it for granted that the recorded fauna of the 'Norwich Chalk' 

 has been derived from pits exclusively in the same zone. Most of 

 the pits named are now inaccessible and cannot be re-examined.] 

 Unfortunately, in discussing the limits of the zones of the Upper 

 Chalk in Norfolk we get very little assistance from the nearest area 

 in which those zones occur again at all freely, i.e. in Sussex and 

 Hants. The zone of B. quadrata south of the Thames is often 

 very fossiliferous, and the zone of B. mucronata is often even 

 more so, both zones being conspicuous for abundance of free- 

 growing Polyzoa, But in Norfolk, and indeed generally on the 

 north of the Thames, both these zones are much less fossiliferous 

 and practically devoid of free -growing Polyzoa. In fact, they 

 present quite a different aspect; they are much more uniform and 

 much finer apparently in texture. It may be only due to increased > 

 depth, but I have always felt tempted to postulate the existence in 

 the Cretaceous sea of a submerged ridge separating the two areas, or 

 basins. The connection of the Norfolk area with the Kiigen sea, 

 which is so marked in the Trimmingham Polyzoa, must have existed 

 at least as early as the age of the chalk round Norwich and near 

 Cromer, in which Homalostega pavonia, described from Rtigen in 

 1839 but not recorded from any other locality except Trimmingham, 

 is quite abundant. Though Polyzoa are abundant at the top of the 



nECADE V. — VOL. III. — NO. I. 2 



